Animator Glitching when skipping from one key frame to another
It is a cyclic dependency.

When you move the foot controler, the console output reads. (Screenshot at the end of the post.) Open the console from the infobar menu: Window > Toggle System Console on windows.

Dependency cycle detected:
  shin.L depends on thigh.L through Parent Relation.
  foot.L depends on shin.L through Parent Relation.
  IKKnee.L depends on foot.L through Parent Relation.
  thigh.L depends on IKKnee.L through IK Constraint.


I suggest parenting the IKKnee bones to the IKFoot bones. Then there will be a hierarchical dependency.